On a similar note, while I normally just stick with bash on Linux (path of least resistance), I really like OpenBSD's ksh. Not quite as small as ash, but still much smaller than either bash or zsh, but with all the essential features (many things people consider bashisms are actually kshisms, and OpenBSD has added many of the ones that truly were bashisms into their version of ksh, since so many scripts have come to rely on them).
